“AUDIBLE SOUND AND VIBRATIONS” SC

Meeting Minutes

Charlotte, NC

March 19, 2008

Chairman: Jeewan Puri

The SC met on Wednesday, March 19 with 11 members and 15 guests present.

WG Report - Sound Level Measurement Guide – Jeewan Puri

WG for writing the Sound Intensity Measurement Guide met on Tuesday, March 19th at 8:00 AM with 8 members and 16 guests present. Four of the guests requested membership of this working group.

Chris Ploetner made a presentation on subject of the Wall Sound Reflection Correction in the IEC Standards. Following Chris, Ramsis Girgis presented the results of recent extensive outdoor and indoor measurements performed by ABB. The presentation identified and quantified the contributors to the difference between transformer noise levels measured using the Sound Pressure level and those measured using the Sound Intensity method. Another objective of this work was determining conditions necessary for accurate measurements using the Sound Intensity method. In conclusion, he recommended that instead of the 8 dB (A) limit in IEC for the difference between Sound Pressure and Sound Intensity measurements that the IEEE Standards adopt the more accurate limit of 4 - 5 dB at each transformer noise frequency component. He also emphasized the improved accuracy provided by adopting the IEC Sound wall reflections correction to sound pressure measurements. Ramsis Girgis and Chris Plotner will use these recommendations to finalize the first draft of the revised Section 13.

It was agreed that Ramsis will modify the present draft of Section 13 for comments from the Working Group for discussions in our next meeting.

Presentation by Ramsis Girgis - 50/60 Hz Sound Level Conversion

Ramsis reported on the results of the survey that he completed on an Appendix on 50/60 Hz within the SC members. He will revise this document according to the comments received and send it for inclusion in an Appendix of C57.12.90. He will circulate the final version copy of this document in the Sub Committee.

Presentation by Ramsis Girgis – Conditions for Sound Intensity Measurements

Ramsis Girgis presented the background and the conclusions of the development of proposed conditions for accurate noise level measurements using the Sound Intensity method. The necessity of the “Environmental Correction factor” for sound pressure measurements was also discussed. IEC standards use the difference between sound pressure and sound intensity measurements as an indicator of environment adequacy for making sound intensity measurements with desired accuracy. These standards stipulate that this difference must not be more than 8dBA for achieving acceptable measurement accuracy. The work presented by Dr. Girgis has evaluated the presently used IEC practices for evaluating measurement environment and concluded that the pressure and intensity difference should be measured only at core vibration frequency and its harmonics. This difference should be less than 4dB.

It was agreed that Dr. Girdgis and Chris Ploetner will propose the next draft for the revision of Section 13 on C57.12.90 & 91 incorporating their recommendations on the acceptable conditions for sound intensity measurements and circulate it to the WG and the SC for their comments. These comments will be discussed in our next meeting. After this the WG will address and update the Sound Level Measurement Guide accordingly.

Old Business

Allen Darwin pointed out that the Sound Abatement Guide C57.136 is going to be due for revision. He proposed that we should remove the contents that do not deal with sound abatement and move them in to the Sound Measurement Guide. The Chairman also proposed that additional information on sound barriers should be included in C57.136.

It was agreed that Allen will review draft 4 of Sound Measurement Guide and propose changes to be made to C57.136 in our next meeting.

There being no new business, the meeting adjourned at 9:15 AM

Jeewan Puri

Chairman - ASVSC